The present invention relates to a camshaft adjuster for an internal combustion engine, wherein the camshaft adjuster is attached on the end of a camshaft and acts as a transmission element to a drive wheel for rotational driving of the camshaft, with an internal wheel locked in rotation with the camshaft and a coaxial external wheel that can rotate relative to the internal wheel, wherein a control valve with a valve slide is provided coaxial to the internal wheel, with the valve slide being provided for controlling a fluid for pressurizing pressure spaces arranged between the internal wheel and the external wheel, in order to adjust the angle between the internal wheel and the external wheel.
A camshaft adjuster of the type named above is known from DE 199 55 507 C2. The camshaft adjuster disclosed here is arranged coaxial to the camshaft in the drive of a camshaft and centered and supported relative to the camshaft by a central screw connection. For this purpose, a screw shaft extending coaxial to the camshaft and into a threaded part is provided, in the center of which a valve slide that can move in the axial direction is supported. The screw shaft arranged coaxial to the camshaft holds the transmission parts, which can rotate relative to each other for the adjustment process, for the camshaft adjuster under axial tension against the camshaft, wherein, as a component of the camshaft, the screw shaft tensioned with a clamping nut forms with this camshaft a component to be processed in common with respect to the radial guide surfaces.
This solution produces the disadvantage that a complicated screw shaft is required, which includes a plurality of tight dimensional tolerances to be realized with complex processes. Furthermore, a clamping nut is required, which takes up additional installation space in extension of the camshaft.
From DE 103 30 449 B3 a camshaft adjuster is known, which has a stator arranged coaxial to the camshaft and a rotor arranged coaxial to the stator. The stator and the rotor are each sealed in the axial direction by a thrust washer. Both the stator and also the rotor are arranged concentric to the camshaft, wherein a valve slide is held so that it can move within a hollow borehole in the camshaft. The stator and a thrust washer, which is arranged adjacent to the stator, are connected to the camshaft with a friction fit via a cylindrical surface.
Disadvantageously, the attachment of the stator and also the thrust washer on the camshaft are associated with high costs in terms of production, because a very precise press fit must be produced, wherein, furthermore, the fatigue strength of the press fit is questionable. In addition, the corresponding radial boreholes in the camshaft and stator must be aligned with each other, which requires precise radial alignment at least of the stator and the thrust washer.
Another embodiment of a camshaft adjuster is known from DE 198 17 319 C2. According to this embodiment, for holding an internal body and also an external body, a central tensioning screw is provided, which is screwed into the camshaft by a threaded connection.
This construction is also disadvantageous in so far as the central tensioning screw must have very complicated contours, which require a plurality of fitting dimensions, in order to guarantee the desired running properties with respect to concentricity and insensitivity to vibrations. The fluid system, which interacts with a valve slide arranged within the central tensioning screw, is similarly a component of the central tensioning screw. Due to the arrangement, there is leakage between the valve slide and the tensioning screw, wherein there is the risk of pistons seizing because the internal body must be pressed onto the tensioning screw. Here, the geometric dimensions of the component change, which negatively affects the required dimensional accuracy for the axial guidance of the valve slide. The entirety of the construction further has a plurality of individual parts, which represent the most unfavorable case with respect to the formation of the tolerance chains. Thus, additional problems arise in the production and the processing of the central tensioning screw. Another problem arises due to the response due to a change in temperature, because a camshaft adjuster is exposed to a considerable thermal load.